Remember last window position (plus size and maximized state)

I'd like to have my app's windows re-open in the same spot as I left it last time.... Just a small nuisance to keep moving it every time I open it.

In macOS, this is the default behaviour, but Fyne apps don't behave like that. Not sure if this should be considered a bug or not.

I'm also aware that this is a desktop responsibility (positioning new windows), and that some Linux window managers have a "Remember" feature, but this is not consistent in all environments.

After briefly discussing this in Fyne's Slack channel, the proposal is to add a feature that would allow the app to request this behaviour, something like window.RememberPosition(). This would of course only work in environments that provide such capability